1. Field of the Invention
The present invention relates generally to systems and methods for controlling turbocharger compressor output temperature in a compression-ignition engine and, in particular, to a system and method for determining the temperature of charge air exiting the turbocharger compressor.
2. Background Art
In a typical compression-ignition engine equipped with an exhaust gas recirculation (EGR) system, a limited amount of exhaust gas is directed into an intake manifold of the engine. This ensures that unused fuel and byproducts are combusted before they are released to the atmosphere, and it also lowers peak combustion temperature to minimize the formation of oxides of nitrogen (NOx). This feature is enhanced by the addition of an EGR cooling system, which reduces the EGR gas temperature before it is introduced into the intake manifold. This increases EGR charge density and reduces overall combustion temperatures and their contribution to the formation of NOx.
In engines so equipped, intake air is commonly compressed and cooled, typically by respectively using a turbocharger compressor and a charge air cooler, to increase power density, that is, the power per swept volume. Added flexibility in the compression of intake air compared with that of a conventional turbocharger compressor is often achieved by using a variable geometry turbocharger (VGT). The flexibility optimizes the turbocharger rotational speed and acceleration, which minimizes turbo lag, the response time required for the turbocharger to begin to affect engine performance following an accelerator actuation. The VGT is typically controlled by an electronic control module (ECM) to supply to the engine amounts of turbo boost that vary depending on various operating conditions.
A concern with compressing intake air is that of overheating the charge air cooler. Accordingly, a dependable and accurate method of determining the output temperature of the compressor is an important factor in preventing such overheating.